How do I use this web app?

Simply choose a classic game you are interested in researching and app will return a list of similar games. If you’d like to restrict the list of inputs to a single system, you can to that with the drop down at the top. If you’d like to restrict the list of systems for comparison in the results list, you can do that with the check boxes at the bottom. Just be forewarned, as you restrict the list of systems to compare to, you may find the quality of results fall quickly unless you are trying to make an apples to apples comparison (i.e. using a hockey game from one system to find hockey games on another).

How does the app decide which games are similar?

The similarity metric is entirely calculated using the text of the Wikipedia articles about each of these games. This is why not every game from these systems is represented here, since not every game had a Wikipedia article. In some cases it’s not a perfect system since multiple games have the same Wikipedia page or, for example, a game may share a Wikipedia page with the movie it is based on.
For more information on how the text was encoded for a similarity calculation, check out the Python module Gensim.

If this app can figure out that basketball games are in some way similar to football games (sports), why isn’t Mario similar to Sonic (mascot platformers)?

If you play around with the app, you’ll quickly find some very cool results as it uncovers Castlevania’s relationship to other vampire related games such as Van Helsing. On the other hand, keep in mind that the method used here is still bound by the words on the Wikipedia pages. While I haven’t studied the words on Sonic and Mario’s pages, most likely they aren’t close enough to establish a relationship between the two. Using Gensim, the words describing two games don’t need to be the same, but they need to share enough similar meaning to establish a relationship.